Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$142.68	11.543%	$159.1496	$159.15	$159.15	$159.10
Purchase #2	$28.56	4.301%	$29.7884	$29.79	$29.80	$29.80
Purchase #3	$104.25	6.395%	$110.9168	$110.92	$110.90	$110.90
Purchase #4	$77.65	3.749%	$80.5611	$80.56	$80.55	$80.60
Purchase #5	$40.93	4.862%	$42.92	$42.92	$42.90	$42.90
Purchase #6	$151.49	10.872%	$167.96	$167.96	$167.95	$168.00
Purchase #7	$74.61	7.862%	$80.4758	$80.48	$80.50	$80.50
7 purchase totals =	$620.17		$671.7717	$671.78	$671.75	$671.80